The present invention relates to a siamese type construction for an internal combustion engine air-fuel mixture intake system, and more particularly relates to such a siamese type construction for an internal combustion engine intake system, said internal combustion engine incorporating two intake valves and thus being of the three valve type or the four valve type, wherein there is provided an intake control valve construction for selectively supplying intake air-fuel mixture to said two intake valves in varying proportions.
The present invention has been described in Japanese Patent Application Ser. No. Showa 61-039550 (1986), filed by an applicant the same as the applicant or the entity assigned or owed duty of assignment of the present patent application; and the present patent application hereby incorporates into itself by reference the text of said Japanese Patent Application and the claim and the drawings thereof; a copy is appended to the present application.
Further, the present inventors wish hereby to attract the attention of the examining authorities to copending patent application Ser. No. 869,890, now U.S. Pat. No. 4,699,104, which may be considered to be material to the examination of the present patent application.
In the prior art, there have been proposed various types of intake passage structures for internal combustion engine cylinder heads and intake systems, and in particular for so called siamese type cylinder heads. In Japanese Utility Model Laying Open Publication Ser. No. 60-45829 (1985), which it is not intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law, there is disclosed an internal combustion engine with, for each of its cylinders, an intake passage structure which incorporates a single initial intake passage portion which then bifurcates into two intake port portions, each one of which then opens to the combustion chamber of said cylinder past a respective one of two separate intake valves provided. Thus, this internal combustion engine incorporates two intake valves for each of its cylinder chambers, and therefore is of the so called three valve type or the so called four valve type. And this type of intake passage construction is typically termed a siamese one, because of the bifurcation or branching of the initial intake passage portion thereof.
Further, in Japanese Utility Model Laying Open Publication Ser. No. 60-92733 (1985), which also it is not intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law, there is disclosed such a so called siamese type intake passage construction, which further is elaborated in that it incorporates, as said two branched intake port passage portions, a generally straight intake passage portion and a generally helical intake passage portion arranged in parallel with said generally straight intake passage portion and axially turning around the valve port which it defines into the combustion chamber so that both said generally straight intake passage portion and also said generally helical intake passage portion receive supply of intake air-fuel mixture from the engine intake manifold. Further, according to a dividing wall or bulkhead construction, a bypass passage is provided closer to the side of the generally straight intake passage portion than to the side of the generally helical intake passage portion, and directly connected with the end of the turning portion of the generally helical passage portion, with an intake control valve selectively at least partially interrupting the flow of air-fuel mixture between said generally straight intake passage portion and said bypass passage near the entrance portion of the intake port construction, as well as selectively isolating their respective entrance portions.
With such an intake passage portion structure for an internal combustion engine cylinder head and intake system, when the intake control valve is controlled to be in the closed state by a control system therefor, which is typically done when the current value of engine load is less than a certain determinate threshold value, substantially all of the air-fuel mixture sucked in by the combustion chamber of the engine is inhaled through the generally helical intake passage portion, and is accordingly imparted with strong swirling. Thus, this mode of operation is appropriate for when the engine is operating at low load, as during the idling engine operating condition. In this condition, because of this swirling motion, the limit to which the air-fuel mixture being supplied to the engine can be weakened without engendering deleterious effects is extended. However, at this time the resistance presented to flow of air-fuel mixture by the generally helical intake passage portion by itself alone is relatively high. On the other hand, when the intake control valve is controlled to be in the open state by the control system therefor, most of the air-fuel mixture sucked in by the combustion chamber of the engine is inhaled through the generally straight intake passage portion and through the bypass passage with only a minor proportion thereof being inhaled through the generally helical intake passage portion, and accordingly the inhaled air - fuel mixture as a whole is imparted with relatively weak swirling, and further the resistance presented to flow of air-fuel mixture by the two passage portions together in parallel is relatively low, thus accordingly causing the volumetric efficiency of the engine to be high so as to develop good engine power output; this mode of operation is appropriate for when the engine is operating at high load such as full load. Thus, by the selective operation of the intake control valve, extra swirl is selectively provided for the intake air-fuel mixture which is being sucked into the combustion chamber of the engine, so as to improve the misting of the fuel and in order to increase the intake air-fuel mixture flow speed, thereby to improve the fuel combustibility, the flame front propagation speed, and the firing efficiency, and thereby to militate against engine knocking, thereby to allow the engine to be operated with a weaker intake air-fuel mixture than would otherwise be practicable.
There is however a problem with such an intake passage portion structure for an internal combustion engine cylinder head and intake system, in that, when the control valve is thus controlled to be in the closed state by its control system and substantially all of the air-fuel mixture sucked in by the combustion chamber of the engine is being inhaled through the generally helical intake passage portion and is accordingly being imparted with strong swirling, although the above described advantages of the air/fuel ratio operating region being extended in the weakness direction, improved fuel combustibility, increased flame front propagation speed and firing efficiency, and improved engine anti knock characteristic are obtained, nevertheless on the other hand the richer portions of the air-fuel mixture are preferentially biased towards the peripheral portions (i.e. the circumferential side portion) of the combustion chamber due to the effect of so called centrifugal force caused due to this swirling action, and the air/fuel ratio at the central portion of the combustion chamber tends to be weaker than at other portions thereof, i.e. tends to be weaker than the overall air/fuel ratio in the combustion chamber as a whole. Since it is typical for the spark plug for such an engine combustion chamber in fact to be mounted at said central portion thereof, the problem arises that air-fuel mixture of a richness sufficient to be ignited by said spark plug is not reliably obtained at said central portion of said combustion chamber around said spark plug, and thereby, particularly when the air/fuel ratio of the overall air-fuel mixture being supplied to the combustion chamber or chambers is near the limit in the weakness direction, the fluctuations of combustion are increased, and torque fluctuations from cycle to cycle of the internal combustion engine are increased due to inferior ignition performance, and thereby particularly the idling operation stability of the engine, and the drivability of a vehicle incorporating it, are undesirably deteriorated.